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64.
Optical emission diagnosis of carbon nanoparticle incorporated chlorophyll for sensing applications
SANKARARAMAN S, SARITHA DEVI H V, RAJ VIMAL, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2019, izvirni znanstveni članek

Opis: Chlorophyll fluorescence (Chl F) is widely used in sensing applications to understand terrestrial vegetation and environmental and climatic variations. The increasing rates of industrialization and carbon emission from internal combustion engines (ICEs) pose a threat to sustainable development. This study analyses the impact of carbon nanoparticles (CNPs) from ICEs on the optical absorption and fluorescence emission of leaf pigments. Leaf pigments without and with CNPs were subjected to UV-visible and photoluminescence (PL) spectroscopy analyses. The field emission scanning electron microscopy and highresolution transmission electron microscopy images of CNPs showed their morphology. The Jablonski diagram of the CNP-incorporated chlorophyll system helped in understanding the fluorescence emission,internal conversion, and the exchange of energy between them. The variations in (i) total chlorophyll, (ii) optical absorbance by total chlorophyll, (iii) PL emission peak (at 675 nm and 718 nm) intensities for different excitation wavelengths, and (iv) normalized absorbance at the PL emission peaks with different CNP concentrations were analysed by dividing into three regions. In Region I (0–0.625 mg ml−1 ), the radiative component dominated the nonradiative component as a result of energy transfer from CNPs to chlorophyll. In Region II (0.625–1.2 mg ml−1 ), the increase in CNP concentration initiated diffusion into chloroplasts, resulting in the increase in the nonradiative part of total energy and decrease in PL peak intensity. In Region III (1.2–2.5 mg ml−1 ), the energy absorbed by the CNPs dissipated more nonradiatively, leading to a slow rate of increase in the radiative part. The visual response of PL emission, color purity, and the distribution of the emitted energy over the spectrum studied with the help of CIE plots, power spectrum, and confocal fluorescence microscopy revealed the fluorescence emission in the red region. This study suggests the possibility of employing Chl F in agricultural, environmental, and biological fields for sensing applications.
Ključne besede: carbon nanoparticle, optical emission, fluorescence
Objavljeno: 05.07.2022; Ogledov: 68; Prenosov: 0
.pdf Polno besedilo (1,92 MB)

65.
Order fluctuation induced tunable light emission from carbon nano system
SANKARARAMAN S, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2019, izvirni znanstveni članek

Opis: The paper reports the thermal-induced order fuctuations, in a carbon nanosystem with carbon nanotubes (CNTs) synthesized by the incomplete combustion of gingelly oil. The sample annealed at diferent temperatures (30–400 °C) is subjected to various morphological and spectroscopic characterizations. The ultraviolet–visible spectroscopic and thermogravimetric analyses reveal the CNTs in the sample. The high-resolution transmission electron microscopy (HR-TEM) also confrms the formation of CNTs in the sample. The Raman spectrum and X-ray difraction pattern show the signature of multi-walled to single-walled CNT transformation and thus an order fuctuation on annealing. The quantum yield of the sample, measured by integrating sphere method, yields 46.15% at an emission wavelength of 575 nm. When the excitation wavelength is varied from 350 to 510 nm, the CIE coordinate moves from the white region to the yellowish-green region. The varying amount of CNTs in the soot, upon annealing is found to vary the luminescence emission from the sample. The study reveals the thermal-induced oscillatory order in carbon nanosystem with carbon nanotubes (CNTs) leading to tunable excitation/ thermal-dependent luminescence emission and thereby suggesting the possibility of converting the futile soot for fruitful applications in photonics and nanoelectronics.
Ključne besede: Carbon nanosystem, Single-walled carbon nanotubes, Multi-walled carbon nanotubes, Raman spectroscopy, Thermogravimetric analysis, CIE plot, Quantum yield, gingelly oil
Objavljeno: 05.07.2022; Ogledov: 79; Prenosov: 0
.pdf Polno besedilo (1,82 MB)

66.
Carbon nanoparticles assisted energy transport mechanism in leaves: A thermal lens study
SWAPNA MOHANACHANDRAN NAIR SINDHU, 2019, izvirni znanstveni članek

Opis: In the world of increasing population and pollution due to carbon emissions, the research for effective utilization of futile diesel soot for fruitful applications has become a necessity for a sustainable development. The contribution to pollution from vehicles and industries due to the aging of engines has caused a crisis. Carbon nanoparticles (CNPs) have been the subject of interest because of their good physical, chemical, and biological properties. The present work investigates the role of CNPs produced by internal combustion engines on the energy transport mechanism among leaf pigments using the sensitive and nondestructive single beam thermal lens technique. The studies reveal the absorption changes by various chlorophyll pigments with the concentration of CNPs sprayed on the leaves. Though for low concentrations CNPs lower the photon absorbance by chlorophyll pigments, the effect gets reversed at higher concentrations. The variation of thermal diffusivity with CNP concentration and its role in the energy transport mechanism among chlorophyll pigments are also studied. It is found that CNP concentrations of 625-2500mg/l are good for better intra-pigment energy transport leading to increased rate of photosynthesis and plant yield and thereby helping in attaining food security. The variation of CNP assisted energy transport among leaf pigments on the production of nicotinamide adenine dinucleotide phosphate (NADPH) and carbohydrates is also studied with ultraviolet (UV) and near-infrared (NIR) spectroscopy.
Ključne besede: carbon nanoparticle, soot, energy transport, thermal lens, photosynthesis
Objavljeno: 05.07.2022; Ogledov: 115; Prenosov: 0
.pdf Polno besedilo (1,84 MB)

67.
Thermal induced order fluctuations in carbon nanosystem with carbon nanotubes
SWAPNA MOHANACHANDRAN NAIR SINDHU, SANKARARAMAN S, 2019, izvirni znanstveni članek

Opis: The allotropes of carbon nanomaterials such as carbon nanotubes (CNTs) and nanoparticles (CNPs) have emerged as a thrust area of research during the last decade because of their unique properties.CNTs are widely used in microelectronic, sensor, bio-imaging, supercapacitors, fuel cell, and etc. applications. In the present work, we report the thermal induced order fluctuations in the CNPs with CNTs synthesized from camphor. The samples annealed to different temperatures are characterized by various spectroscopic techniques such as UV–Visible, Raman, Fourier Transform Infrared, and Xray Photoelectron Spectroscopy. Samples’ structure and morphology are analyzed by scanning and transmission electron microscopes, and X-ray diffraction. The thermogravimetric analysis indicates not only the mass variation upon annealing but the thermal stability also. The spectroscopic and thermal analyses reveal the thermal induced oscillations in the carbon system which can be assigned to the dynamics in CNTs through desorption of hydrogen/ thinning or shortening of multi-walled CNTs/sp2 - sp3 conversions and the removal of amorphous carbon (AC). Since the amount of CNTs in the sample decides the electrical behavior, the sample can be tuned to a desired electrical conductivity by annealing and thus making it a tunable material for electronic applications.
Ključne besede: Carbon nanotubes, Camphor, Thermal induced oscillations
Objavljeno: 05.07.2022; Ogledov: 69; Prenosov: 0
.pdf Polno besedilo (2,75 MB)

68.
Soot as a precursor for the low temperature synthesis of organometallic sodium carbide
SANKARARAMAN S, SARITHA DEVI H V, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2019, izvirni znanstveni članek

Opis: The carbonaceous soot finds a wide range of applications in many fields due to the richness of various allotropes of carbon. The present work explores the possibility of least investigated sodium carbide (Na2C2) as a potential semiconducting material for photonic applications. The soot, formed by the incomplete combustion of gingelly oil is taken as the carbon precursor for the low-temperature synthesis of the industrially significant organometallic Na2C2. The morphological modifications are analyzed using High-Resolution Transmission Electron Microscope and elemental study is carried out by Energy Dispersive Spectroscopy and x-ray dot mapping. The formation of Na2C2 is primarily identified from x-ray powder diffraction pattern and further confirmed by other structural and thermal analysis techniques such as Fourier Transform Infrared, Raman spectroscopy, and Thermogravimetry. The region of optical absorption, bandgap, as well as its emission properties are studied by recording the Ultraviolet-Visible and Photoluminescence spectrum. The Tauc plot analysis suggests its semiconducting nature with direct bandgap energy of 2.08 eV. The analysis with the help of CIE, and power spectrum reveal a prominent blue emission around 440 nm irrespective of excitation in the UV region. Thus, the major highlights of this work lie in two factors- firstly, the effective utilization of the soot and secondly, easier low-temperature and cost-effective synthesis of semiconducting Na2C2 for photonic applications.
Ključne besede: carbonaceous soot, sodium carbide, photonic applications
Objavljeno: 05.07.2022; Ogledov: 103; Prenosov: 0
.pdf Polno besedilo (1,33 MB)

69.
Generalized Theory of Thermal Conductivity for Different Media: Solids to Nanofluids
SANKARARAMAN S, SWAPNA MOHANACHANDRAN NAIR SINDHU, 2019, izvirni znanstveni članek

Opis: The advent of nanotechnology in the 21st century opened a new branch of nanoscience known as nanofluids, finding a wide range of industrial applications especially in heat transfer. Though the theory of thermal conductivity of solids is well established, there is no such conclusive model to explain the thermal conductivity of nanofluids. In the present work we propose a generalized theory for thermal conductivity applicable to materials ranging from heterogeneous solids, porous materials, nanofluids, and ferrofluids. The model could explain the effective thermal conductivity of not only the combination of solids but also solid−fluid mixtures. The proposed theory could successfully link the existing models for porous solid materials and nanofluids as its special cases. The proposed model is verified against experimental data by simulating the theoretical equations
Ključne besede: thermal conductivity, generalised model, Sankar-Loeb model
Objavljeno: 05.07.2022; Ogledov: 112; Prenosov: 0
.pdf Polno besedilo (3,99 MB)

70.
Time series analysis of duty cycle induced randomness in thermal lens system
SWAPNA MOHANACHANDRAN NAIR SINDHU, 2020, izvirni znanstveni članek

Opis: The present work employs time series analysis, a proven powerful mathematical tool, for investigating the complex molecular dynamics of the thermal lens (TL) system induced by the duty cycle (C) variation. For intensity modulation, TL spectroscopy commonly uses optical choppers. The TL formation involves complex molecular dynamics that vary with the input photothermal energy, which is implemented by varying the duty cycle of the chopper. The molecular dynamics is studied from the fractal dimension (D), phase portrait, sample entropy (S), and Hurst exponent (H) for different duty cycles. The increasing value of C is found to increase D and S, indicating that the system is becoming complex and less deterministic, as evidenced by the phase portrait analysis. The value of H less than 0.5 conforms the evolution of the TL system to more antipersistent nature with C. The increasing value of C increases the enthalpy of the system that appears as an increase in full width at half maximum of the refractive index profile. Thus the study establishes that the sample entropy and thermodynamic entropy are directly related.
Ključne besede: Time series analysis Fractal analysis Photothermal lens spectroscopy Fractal dimension Hurst exponent Sample entropy
Objavljeno: 05.07.2022; Ogledov: 86; Prenosov: 0
.pdf Polno besedilo (1,30 MB)

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